The present invention generally concerns a curable chlorinated polyethylene elastomer composition having improved resistance to ozone-induced cracking. More particularly, the present invention concerns a curable chlorinated polyethylene composition which, after vulcanization, by press curing, with a peroxide compound under extreme conditions, e.g., at a temperature of 204.degree. Centigrade for a period of ten minutes, resists ozone-induced cracking for a period of at least 168 hours in a severe test environment. The "severe test environment" is described in detail hereinbelow.
Vulcanization or curing of saturated, halogen-containing polymers such as chlorinated polyethylene is a well known process. Such curing generally takes place either with a non-peroxide compound and a base or with a peroxide compound and a vulcanization accelerator.
It has been discovered that ozone resistance, as defined by the absence of cracking, of peroxide-cured chlorinated and chlorosulfonated polyethylene materials varies considerably depending upon a number of factors. One factor is the amount of moisture present during ozone testing. For example, some materials have an ozone resistance in excess of one hundred hours when tested in the absence of moisture. The same materials will have an ozone resistance of five hours or less when tested at a relative humidity of 50% or more. A second factor is found in the combination of time and temperature used to cure the materials. For example, a material cured at a temperature of 177.degree. Centigrade for a period of twenty minutes may have satisfactory ozone resistance whereas the same material cured at a temperature of 204.degree. Centigrade for a period of ten minutes cracks in only a few hours under severe ozone test conditions. A third factor is the cure package used to effect vulcanization of the materials.
It would be desirable if there were available a vulcanizable chlorinated polyethylene composition which, after curing, exhibited resistance to ozone-induced cracking for a period of 168 hours or more in a severe ozone test environment, particularly when such curing takes place under extreme conditions, e.g., at a temperature of 204.degree. Centigrade for a period of ten minutes.
It would also be desirable if such a compound also exhibited good processing and rubber-like properties suitable for use in the manufacture of hoses, tubing, molded goods and wire and cable insulation/jackets.